Onchocerciasis - river blindness

Fact sheet N°95

Onchocerciasis -- the world's second leading infectious cause of blindness -- is
present in 36 countries of Africa, the Arabian peninsula and the Americas. As a public
health problem the disease is most closely associated with Africa, where it constitutes a
serious obstacle to socio-economic development. Onchocerciasis is often called "river
blindness" because of its most extreme manifestation and because the blackfly vector
abounds in fertile riverside areas, which frequently remain uninhabited for fear of
infection.

Prevalence

Out of some 120 million people world-wide who
are at risk of onchocerciasis, 96% are in Africa.

Of the 36 countries where the disease is endemic, 30 are in sub-Sahara Africa (plus
Yemen) and six are in the Americas.

A total of 18 million people are infected with the disease and have dermal
microfilariae, of whom 99% are in Africa.

Of those infected with the disease, over 6.5 million suffer from severe itching or
dermatitis and 270 000 are blind.

Characteristics

Onchocerciasis is caused by Onchocerca volvulus, a parasitic worm that lives for
up to 14 years in the human body. Each adult female worm, thin but more than 1/2 metre in
length, produces millions of microfilariae (microscopic larvae) that migrate throughout
the body and give rise to a variety of symptoms: serious visual impairment, including
blindness; rashes, lesions, intense itching and depigmentation of the skin; lymphadenitis,
which results in hanging groins and elephantiasis of the genitals; and general
debilitation. Onchocerciasis manifestations begin to occur in persons one to three years
after the injection of infective larvae.

Microfilariae produced in one person are carried to another by the blackfly, which in
West Africa belongs to the Simulium damnosum species complex. The blackfly lays its
eggs in the water of fast-flowing rivers. Adults emerge after 8-12 days and live for up to
four weeks, during which they can cover hundreds of kilometres in flight.

After mating, the female blackfly seeks a bloodmeal and may ingest microfilariae if the
meal is taken from a person infected with onchocerciasis. A few of these microfilariae may
transform into infective larvae within the blackfly, which are then injected into the
person from whom the next meal is taken and subsequently develop into adult parasites,
thus completing the life cycle of the parasite.

The Onchocerciasis Control Programme (OCP)

OCP was the first major programme developed to control onchocerciasis. It was launched
in 1974 in an area that originally encompassed seven countries in West Africa. In 1986 the
programme was extended to include four additional countries, bringing the current total of
participating countries to 11. The total operational area covers 1.23 million sq. km and a
combined population of about 30 million people.

The programme has been jointly sponsored by WHO, the World Bank, the United Nations
Development Programme and the Food and Agriculture Organization and is supported by a
coalition of more than 20 donor countries and agencies. WHO acts as the Executive Agency
for the programme, while the World Bank is responsible for mobilizing resources and
administering the OCP Trust Fund. The Programme is scheduled to come to an end by the year
2002. The estimated total cost for the programme will be US$550 million, or less than US$1
per year for each protected person.

OCP's principal method for controlling onchocerciasis has been to break the
cycle of transmission by eliminating the black fly. Simulium larvae are destroyed by
application of selected insecticides through aerial spraying of breeding sites in
fast-flowing rivers. Once the cycle of river blindness has been interrupted for 14 years
the reservoir of adult worms dies out in the human population, thus eliminating the source
of the disease. The parasite reservoir has now virtually died out in the original
7-country operations area (map) and will be largely eliminated in the remaining four
countries by the year 2002. To complement vector control activities, OCP now distributes
the drug ivermectin where needed in the operations area through a community directed
approach. Ivermectin kills the larval worms that cause blindness and other onchocercal
manifestations and acts to decrease transmission as well.

Programme achievements

At OCP's launch, more than 1 million people in
West Africa suffered from onchocerciasis, of whom 100 000 had serious eye problems
including 35 000 people who were blind. Today, the number of infected people within the
original area of operations is practically nil and vector control efforts have almost
ceased.

Some 1.5 million people who were once infected with onchocerciasis no longer have any
trace of the disease. Eleven million children born in the operational area since the
programme's inception are now free of risk of contracting the disease.

At the turn of the century it was estimated that OCP had prevented almost 300 000 cases
of blindness in the 11 countries involved in the programme.

The successful vector control activities are opening up an estimated 25 million
hectares of fertile riverine land for resettlement and cultivation, land that was
previously deserted for fear of onchocerciasis. This land has the potential to feed an
additional 17 million people annually through the use of indigenous technologies and
farming practices.

Global control strategy

The development of ivermectin in the 1980's provided for the first time a safe,
effective drug capable of reducing the numbers of skin microfilariae in infected people
and resulting in clinical improvement and decreased transmission of infection. As a
result, a new global strategy for controlling onchocerciasis has now been defined that is
based on:

yearly administration of single doses of ivermectin to affected populations.

In 1987 ivermectin's manufacturer, Merck & Co., Inc., pledged to provide at
no cost all the drug necessary for as long as necessary to overcome onchocerciasis
as a public health problem. It established the Mectizan® Donation Program which has
collaborated with WHO, health ministries and non-governmental development organizations
(NGDOs) so that between 1987 and the end of 1996, more than 65 million doses of Mectizan®
had been donated for distribution.

Onchocerciasis Elimination Program in the Americas (OEPA)

To coordinate onchocerciasis control efforts in the 6 endemic countries of the Americas
and to reach the goal of eliminating first the pathology and then the disease, the
Onchocerciasis Elimination Programme for the Americas (OEPA) was created in 1992 with the
support of PAHO, the Inter-American Development Bank, a consortium of NGDOs, and all of
the affected countries.

The African Programme for Onchocerciasis Control (APOC)

The outstanding success of the Onchocerciasis Control Programme (OCP), when expressed
in health, economic and development terms, was the motivating rationale for the launching
of a new programme, African Programme for Onchocerciasis Control (APOC) in December 1995.
APOC shares the same co-sponsoring agencies and donors with the OCP.

Unlike the OCP, the new Programme, APOC is non-vertical and based on a full partnership
between affected communities, the participating governments, a consortium of international
non-governmental development organizations (NGDOs) and bilateral agencies.

The Programme's objective is to establish, within a period of 12 years, sustainable
community-directed ivermectin (Mectizan®) distribution systems covering about 50 million
people in 19 countries outside the OCP where onchocerciasis still is a serious public
health problem. These countries are: Angola, Burundi, Cameroon, Chad, the Central African
Republic (CAR), the Congo, the Democratic Republic of the Congo, Ethiopia,
Equatorial-Guinea, Gabon, Kenya, Liberia, Malawi, Mozambique, Nigeria, Rwanda, Uganda,
Sudan and Tanzania.

In these countries, it is estimated that of the 15 million heavily infected people, 6.4
million live in areas where the parasite strains are a major cause of blindness while 8.6
million live in areas where the parasite strains are responsible for severe skin disease
associated with grave and unrelenting itching.

APOC partners share responsibilities in implementing the Programme's principal control
strategy which is based on community directed treatment with ivermectin (CDTI). Where
feasible, ivermectin treatment will be complemented with vector elimination using
environmentally safe methods.

Since its inception, the Programme management has been set up at the OCP headquarters
and National Onchocerciasis Task Forces (NOTF) have been created in 14 countries. The
Memorandum (a multilateral agreement) has been signed by 19 countries and 13 donors
bringing the programme legally into force as of April 1996. At the end of 1999, 12
national plans for the control of onchocerciasis had been developed and 57 projects were
approved for funding, including: ivermectin distribution projects (48), vector elimination
projects (4) and projects for strengthening NOTFs' secretariats (5). Thirty-eight of these
projects have already been started.

In 1996, the NGDO Coordination Group facilitated distribution to 7.5 million people.
This number increased to 11.7 million in the first year of APOC's field activities
(1997-1998) and was expected to rise to over 15 million by the end of 1999. This constant
increase, as well as close working relationships amongst all APOC partners will enable
APOC to achieve its goal of treating about 45 million people by the year 2007.

Challenges ahead for OCP and APOC

When OCP comes to an end in the year 2002, its present strategy of aerial larviciding
will no longer be applicable. However, some OCP countries are already benefiting from
ivermectin distribution as the only control method. These will continue with ivermectin
treatment, sharing the same control strategy and challenges with APOC. The challenges
include:

(i) Developing with the affected communities, competent
delivery systems to serve as example for the delivery of other drugs to control other
tropical diseases.

(ii) While the OCP towards its end is aiming at having the devolved activities
integrated into the varied health systems, APOC is aiming at devolving all aspects of
control operations into the health systems from the onset, in participating countries. The
two programmes will share experiences on this issue.

(iii) Finally, APOC has an additional challenge, to demonstrate the effectiveness of
its unique partnership in implementing a sustainable solution to a public health and
development problem.